This invention relates to magnetic valves in general and more particularly to an improved circuit for determining the minimum operating current (response current) of magnetic valves.
The response current of relays is measured by applying a staircase voltage to the field coil of the relay. When the relay finally responds, the further advance of the staircase supply voltage is interrupted by a contact of the relay, and the value of the response current can be read on a measuring device. The response indication thus is accomplished by the relay to be measured itself.
In principle, the response current of magnetic valves could also be determined in this manner. Because of the delay in the response indication caused by the mechanism of the relay, and the advancing of the supply voltage in staircase steps, this manner of determining the response current yields values which are too inaccurate, particularly if the response current of the magnetic valve is also to be used for indirectly determining the pressure in the fluid line which is shut off by the magnetic valve. This problem comes up frequently in the diagnosis of motor vehicles, having engines which operate with fuel injection and which also contain hydraulic systems controlled by magnetic valves. By determining the fluid pressure indirectly via the response current of the magnetic valves, expensive pressure pickups can be saved.